1. Field of the Invention
The present invention relates to a method for compression molding.
2. Background of the Related Art
Compression molding process has been previously used for processing high polymer material. The compression molding method is performed by making a mold of a desired pattern of metal material and then compressing a high polymer material within the mold. The high polymer material should have flowability because it should enter and fill the mold by pressure applied to the high polymer material. To ensure such flowability, a transfer path of both the mold and the high polymer material is maintained at high temperature above a glass transition temperature of the high polymer material. Once the high polymer material conforms to the mold of the desired pattern, it is cooled for a certain amount of time to eliminate flowability of the high polymer. The high polymer material is then solidified, and the mold is removed to produce the solid high polymer product having the mold pattern.
FIG. 1 is a schematic view of a related art compression molding press. The related art compression molding press will now be described.
The related art compression molding press includes a press support 1, a plate induction axis 2, an upper press plate 6, and a lower press plate 5. The press support 1 is located at the bottom of the press, and the press plate induction axis 2 is fixed to both sides of the press support 1. The upper press plate 6 and the lower press plate 5 are fixed on the press plate induction axis 2 to be opposed each other. The upper press plate 6 is fixed on the induction axis 2 and the lower press plate 5 is fixed to ascend and descend along the induction axis 2. The upper and lower press plates 5 and 6 also have the capability for internal temperature adjustment.
A mold support 8a to which a mold 9 is fixed is located on the bottom of the upper press plate 6. A test piece support 8b is fixed on the lower press plate 5 to support a test piece 10.
A pressure device 3 is fixed on the center of the upper side of the press support 1 to allow a flange 12 to reciprocate the lower press plate 5 relative to the fixed upper press plate. A pressure gauge is attached to one side of the pressure device 3 to check pressure when operating the pressure device 3.
A related art compression molding method will now be described. The related art compression molding method is performed using the related art compression molding press as shown in FIG. 1. FIGS. 2a to 2c are sectional views illustrating the related art compression molding method.
As shown in FIG. 2a, the test piece 10 on which a high polymer thin film 11 is deposited is positioned on the test piece support 8b. The mold 9 with a pattern of dots or lines of about 25 nm is positioned on the mold support 8a. Polymethylmethacrylate (PMMA) polymer is used as the high polymer thin film 11.
The mold 9 and the test piece 10 (i.e., a resist) are heated at a temperature (about 200.degree. C.) above the glass transition temperature. As shown in FIG. 2b, the mold 9 and the test piece 10 are compressed so that the pattern of the mold 9 can be molded on the high polymer thin film 11 of the test piece 10. When the temperature of the mold 9 and the test piece 10 are decreased to reduce the PMMA below the glass transition temperature of the PMMA, the mold 9 is separated from the test piece 10. As shown in FIG. 2c, the molded high polymer thin film 11 is etched by anisotropic etching to form a final pattern.
In another related art compression molding process, a high polymer material is heated to a high temperature above its glass transition temperature. Under these circumstances, the high polymer material contacts an inner wall of a mold and adheres to a surface of the inner wall of the mold. As a result, the high polymer material is not likely to be separated from the inner wall of the mold even after this process is completed. To prevent this problem, in this related art compression molding process, a mold release agent is applied to the surface of the inner wall of the mold. Chemical materials such as organosilicon compounds are used as the related art mold release agent.
As described above, the related art compression molding methods have various disadvantages. When the dimension of the pattern is large, an adhesion property at the interface between a mold surface and a high polymer material can be removed using the organosilicon mold release agent. Disadvantageously, if the mold release agent is applied to the surface of the mold embossed or engraved with a pattern having fine granularity of 1 micron or less, the mold release agent is thicker than the dimension of the pattern so that the fine pattern on the mold becomes covered by the mold release agent. As a result, the desired fine pattern cannot be imprinted. Further, even though the pattern is transferred to the substrate, the pattern is not exactly imprinted at a desired position and dimension because of the thick mold release agent that exists on the mold surface. In addition, if related art compression molding methods are performed at high pressure, the substrate to which the pattern is to be transferred and the mold substrate may physically be damaged, so that the pattern fails to be transferred to the substrate. Finally, when the pattern transferred to the surface of the high polymer is varied or distorted with a pattern dimensioned in the range of about 1 micron, there exists no technology to remove this defect or to adjust the dimension of the pattern at such dimensions when the pattern transfer has already completed by compression molding.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.